Maximizing the sustainability of macroalgae biorefinery: A superstructure optimization of volatile fatty acid platform

Macroalgae are a valuable energy source that can be transformed into numerous products most notably fuels and chemicals due to their high content of carbohydrates, proteins, and vitamins. In order to use the macroalgae in a commercial scale, it is necessary to evaluate various potential pathways into value-added products as well as intermediate components and technologies. Furthermore, the potential processes must be designed with minimum carbon and other waste emissions, while simultaneously have to be economically competitive to operate. This in turn presents a large decision-making problem with a significant combinatorial complexity. In order to address this problem this study utilizes a superstructure process design approach for a seaweed biorefinery producing mixed alcohols and mixed organic acids via anaerobic digestion/volatile fatty acid route. Seventeen design alternatives have been proposed to determine the optimal design and technical feasibility by maximizing the net present value in the most environmentally beneficial fashion. The results indicate that biofuel production from macroalgae is economically viable at a minimum ethanol selling price of $1.18/gal. Furthermore, the optimal design enables a 90% reduction in carbon dioxide emissions. Sensitivity results show that seaweed price is the most important parameter that can contribute in improving the economics, thereby confirming that the cost-effective and efficient large-scale seaweed cultivation is utmost important to the success of macroalgae based biofuel production.